The overall goal of the proposed research is to better understand the signaling events that pattern the developing limb and kidney. The Bone Morphogenetic Proteins (BMPs) as well as their antagonists are important in specifying pattern during development. Gremlin is a BMP antagonist that has been shown to be expressed in multiple regions of the developing embryo and appears important in limb development. In order to test whether Gremlin was required for correct embryonic development, a targeted mutation was generated. Homozygotes have two main phenotypes: limb malformation and renal agenesis. The study of limb patterning has provided many insights into how molecular signaling networks might act to correctly produce appropriate cell fate. The failure of correct signaling in the limb results in limb results in limb anomalies, a common congenital malformation. To study the limb malformations in Gremlin mutant mice, an array of molecular markers will be analyzed for changes in gene expression. Over expression analysis in in vitro limb cultures will address Gremlin's relationship with other patterning molecules. In another set of experiments, the cause of the renal agenesis will be investigated. First, careful analysis of molecular markers will attempt to define exactly where and when the defect occurs in nephrogenesis. In vitro cultures of metanephric mesenchyme and ureteric buds will define in which tissue Gremlin is required and further test the mechanism of Gremlin action. The applicant is a clinician scientist who is board certified in Pediatrics and is currently affiliated with the Department of Pediatrics at UCSF Medical Center. He has initiated this project with support from the Pediatric Scientist Development Program grant and intends to complete the analysis of the Gremlin mutant with support from this application. The research will be conducted in the laboratory of Richard M. Harland at UC-Berkeley who heads a laboratory that utilizes multiple model systems to better understand vertebrate development. The research proposed will provide important training in the analysis of targeted mutations in the mouse as well as protein biochemistry which will prove crucial for the applicant when he becomes an independent investigator, his long-term goal.